Chlorine (Cl.sub.2), bromine (Br).sub.2, and bromine chloride (BrCl) are well known in the water treatment industry as effective biocides. At the present time, chlorine, bromine and chloride or bromide-containing molecules capable of undergoing hydrolysis to produce hypohalous acid are the choices of most commercial practitioners of water treatment. These choices however, are not without some serious drawbacks.
Chlorine, which is the most popular choice as a biocide, is disadvantaged as it can form long-lived toxic chloramines with ammonia, which could very well be present in the water to be treated. Laboratory studies have indicated that chloramines in concentrations as low as 0.1 parts per million (ppm) can produce fish kills. Also when using chlorine in water treatment, the production of hypochlorous acid (HOCl) can lead to the formation of other chlorinated nitrogen-containing compounds which can persist to cause environmental damage should the treated water be released into the environment.
Bromine, though not always the biocide of choice, has advantages over chlorine. Hypobromous acid (HOBr) and bromamines are known to be very effective bactericides and viricides. Furthermore, disinfection of the water using selected bromine-containing species can often be achieved with lower residual levels of bromamine and HOBr than with chlorination. Bromamines also decompose very rapidly, hence their discharge levels in water treated with bromine are very low, even in once-through cooling applications.
When dissolved in a large quantity of water, essentially all of the bromine in BrCl forms hypobromous acid (HOBr) as compared to about one-half of the bromine present when elemental Br.sub.2 is used. These and other advantages of bromine chloride are illustrated in Kamlet U.S. Pat. No. 2,662,855 which is incorporated herein by reference.
At the present time, commercial use of BrCl is thwarted by practical considerations. If neat BrCl is used to treat water, there are significant handling problems to overcome. If the BrCl is dissolved in water to overcome such handling problems, the resultant solution is not suitable for long-term use as the hypobromous acid formed therein will soon decompose. Also the amount of BrCl which can be solubilized in water is relatively small, i.e. only about 8.5 grams of BrCl per 100 grams of water at 20.degree. C.